A BOTTOM-UP APPROACH: COMPLIMENTING NMR RELAXOMETRY WITH THEORY AND SIMULATIONS

Angel Mary Chiramel Tony (University of Rostock, Germany)

LinkedIn: @Angel Mary C T; X: @AngelMaryCT1; Bluesky: @angelchirameltony.bsky.social

Abstract: By using Fast Field Cycling (FFC) NMR spectroscopy, dynamical processes can be studied over many orders of magnitude. However, interpreting FFC-NMR data often requires models that are specific to certain systems. Here we propose a novel approach for computing the inter- and intramolecular contribution to the magnetic dipolar relaxation from molecular dynamics (MD) simulations. This method is enabling us to predict NMR relaxation rates, addressing the full FFC frequency range, covering many orders of magnitude, while also avoiding influences due to limitations in system size and the accessible time interval. Our methodology is based on combining the analytical theory of Hwang and Freed (HF) for the long-range intermolecular contribution of the magnetic dipole-dipole correlation function with MD simulations. Here we apply this approach to compute the inter- and intramolecular NMR relaxation of 19F nuclei in the ionic liquid C5Py-NTf2 to study the dynamics of the NTf2 anion. By employing our MD simulation-based approach, we could show that the correlation functions due to the HF theory does asymptotically converge with our MD simulation results at long times. This approach is successful in disentangling the different contributions to the intramolecular 19F-NMR relaxation rate due to the complex intramolecular dynamics of the anion. We successfully described the rotational anisotropy, differentiating between the overall tumbling of the anion and internal rotation of the CF3 group, which is difficult to decipher with the fitting models.